Automotive system for dynamically determining road adhesion

Abstract

A system for determinng the road adhesion of a tire installed on a road wheel of an automotive vehicle operating on a roadway includes a road wheel turn angle measuring device, a vehicle speed measuring mechanism and a steering force measuring mechanism. Information regarding turn angle, vehicle speed and steering force are fed into a processor which determines the road adhesion of the tire.

I claim: 
     
       1. A system for determining the road adhesion of a tire installed on a road wheel of an automotive vehicle operating on a roadway, comprising; road wheel turn angle measuring means comprising means for producing a first signal representing the turn angle at which the steering system of said vehicle is being operated;   vehicle speed measuring means comprising means for producing a second signal representing the speed at which said vehicle is being operated;   steering force measuring means comprising means for producing a third signal representing the steering force required to operate the steering system of said vehicle at said measured road wheel turn angle and said measured vehicle speed; and   processor means for determining the road adhesion of said tire, with said processor means comprising means for receiving said first, second, and third signals and means for deriving from said signals a fourth signal representing the magnitude of said road adhesion.   
     
     
       2. A system according to claim 1 wherein said processor means determines road adhesion by matching measured road wheel turn angle, vehicle speed and steering force with one of a plurality of reference triads comprising road wheel turn angle, vehicle speed and steering force values, where each of such reference triads corresponds to a predetermined value of road adhesion, and by reading a corresponding value for said fourth signal depending upon the results of said matching. 
     
     
       3. A system according to claim 2 wherein said processor means comprises a read-only memory containing said reference triads and said fourth signal values. 
     
     
       4. A system according to claim 1 wherein said road wheel turn angle measuring means comprises an electro-optical angle measuring means operatively connected with a steering system for controlling said road wheel with said angle measuring means being responsive to movement of a steering handwheel. 
     
     
       5. A system according to claim 1 wherein said processor means determines road adhesion by operating upon said first, second and third signals with a mathematical function contained in said processor. 
     
     
       6. A system according to claim 1 wherein said vehicle speed measuring means comprises a signal generator driven by a powertrain of said vehicle. 
     
     
       7. A system according to claim 1 wherein said steering force measuring means comprises a pressure transducer interposed between a steering gear for steering said road wheel and a hydraulic pump for powering said steering gear. 
     
     
       8. A system according to claim 1 wherein said steering force measuring means comprises a torque sensor for sensing torque applied to a driveshaft of a steering gear for steering said road wheel. 
     
     
       9. An emergency operating system for determining the road adhesion of a tire installed on a road wheel of an automotive vehicle operating on a roadway, comprising: road wheel turn angle measuring means comprising means for producing a first signal representing the turn angle at which the steering system of said vehicle is being operated;   vehicle speed measuring means comprising means for producing a second signal representing the speed at which said vehicle is being operated;   steering force measuring means comprising means for producing a third signal representing the steering force required to operate the steering system of said vehicle at said measured road wheel turn angle and said measured vehicle speed; and   Processor means for determining the road adhesion of said tire, with said processor means comprising means for receiving said first, second, and third signals and means for deriving from said signals a fourth signal in the event that the magnitude of said road adhesion is less than a threshold value; and   emergency control means responsive to said fourth signal for operating an emergency control system.   
     
     
       10. A system according to claim 9 wherein said emergency control system comprises means for regulating the operation of a brake system incorporated in said vehicle. 
     
     
       11. A system according to claim 9 wherein said emergency control system comprises means for warning the driver of said vehicle that road adhesion is less than said threshold value. 
     
     
       12. A system according to claim 9 wherein said emergency control system comprises means for limiting the maximum speed of the vehicle. 
     
     
       13. A system according to claim 9 wherein said emergency control system comprises means for limiting the maximum forward acceleration of the vehicle. 
     
     
       14. A system according to claim 9 wherein said emergency control system comprises means for operating an adjustable suspension system. 
     
     
       15. A system according to claim 14 wherein said emergency control system comprises means for controlling damping produced by said adjustable suspension system. 
     
     
       16. A system according to claim 9 wherein said emergency control system comprises means for controlling the output of a power assist device associated with said steering system. 
     
     
       17. A system according to claim 16 wherein said means for controlling the output of a power assist device associated with said steering system comprises a valve for limiting the magnitude of the assist produced by said power assist device.